Four other commanders were transferred last Thursday, based on what Police Commissioner William Bratton said was information developed in the investigation.

The probe is examining whether police officers received gifts and travel from businessmen in exchange for unspecified favors, and has centered on two businessmen, Jona Rechnitz and Jeremy Reichberg, according to a source familiar with the matter who was not authorized to speak publicly.

Rechnitz contributed to de Blasio's 2013 campaign, while Reichberg helped raise money for a nonprofit organization controlled by de Blasio advisers to support the mayor's agenda.

The investigation has also included former Chief of Department Phillip Banks, once the police department's highest-ranking uniformed officer, and Norman Seabrook, head of the correction officers union, the source said.

De Blasio said on Monday he had not conferred with legal counsel because he had not had any contact with federal authorities.

"I assume they have my phone number if they want to talk to me," he said.

The investigation led on Friday to the arrest of a former restaurant owner, Hamlet Peralta, for running a $12 million Ponzi scheme. The source said the case was linked to the probe, though court documents do not specify how.